Control of the HCl Emissions from the Combustion of PVC by In-Furnace Injection of Calcium-Magnesium-Based Sorbents

Abstract

This is a laboratory study on the reduction of hydrochloric acid (HCl) emissions from the combustion of poly(vinyl chloride) (PVC), by in-furnace injection of calcium- and magnesium-based sorbents. Experiments were conducted in a nearly isothermal, electrically heated, drop-tube furnace, at gas temperatures of 850 and 1050°C. PVC and the sorbents were premixed in powder form and injected in the furnace, where combustion of the fuel, release of HCl, and chlorination of the sorbents took place. Combustion was globally fuel-lean, with bulk equivalence ratios in the range of 0.2–0.5; particle heating rates were 104–105 K/sec; gas residence times were ≈1 sec. Experiments burned pure pulverized PVC (to serve as a baseline) or PVC mixed with pulverized Ca(OH)2, Mg(OH)2, calcium acetate (CA), magnesium acetate (MA), calcium-magnesium acetate (CMA), calcium formate (CF), calcium propionate (CP), and calcium benzoate (CB). The particle size of PVC was in the range of 125–150 μm, the size of the sorbents varied but it was typically <100 μm. The Ca/Cl or Mg/Cl molar ratios were set to 1:2, reflecting a stoichiometric composition, except for CMA where the Ca/Cl ratio was set to either 1:6 or 1:3. The HCl reduction efficiency of the sorbents in these runs ranged from 3% to 98%. The calcium-based sorbents exhibited high HCl capture efficiencies (72–98%), especially the organic salts (89–-98%). The latter compounds, upon de volatilization of their organic components, formed high-porosity cenospheric particles, which imposed minimal mass diffusion limitations. The magnesium-based sorbents did not react significantly (3–5%) with HCl in this temperature range. However, a considerable fraction of the magnesium in CMA appears to have taken part in the chlorination reaction. Varying the gas temperature between 850°C and 1050°C did not significantly affect the HCl capture efficiency of the sorbents. Key words: HCl emissions; PVC combustion; clacium-based sorbents for HCl capture; calcium-magnesium-acetate (CMA)